This invention pertains generally to a method of testing an electron discharge device, and particularly to a method for testing of an electron discharge device that uses an indirectly heated cathode electrode.
It is known in the art that the types of electron discharge devices known as traveling wave tubes (TWTs) may be used as power amplifiers in transmitters carried by guided missiles (referred to hereinafter simply as "missiles") that incorporate active guidance systems. Although the electrical parameters of any type of TWT for such an application may be conventional, there are stringent ancillary requirements that must be met by any satisfactory type of TWT used in missiles. In particular, a TWT for a missile must be: (a) adapted to be changed from a dormant (or "OFF") condition to an operative (or "ON") condition in a relatively short period of time (say, one second); and (b) adapted to maintain a vacuum at a designed level for a long period of time in a dormant condition (say, a pressure no greater than 1.times.10.sup.-6 torr for a period of ten years).
Unfortunately, it is not feasible to manufacture TWTs that may be guaranteed to maintain a desired degree of vacuum for years. It is more economical to manufacture TWTs following state of the art practices and replace any TWT that becomes "soft"; i.e., loses the desired level of vacuum. It has been found, however, that field testing for the level of vacuum in a TWT requires that the TWT be turned "ON", a state that may not be tolerated in many tactical situations.
In addition to the foregoing, it is necessary on occasion to determine the state of the electron-emitting surface of a cathode in TWT that has been in storage or inoperative for a long period of time. According to the prior art, the state of an electron-emitting surface of the cathode would be determined by operating the TWT. A test specifically directed to determining the state of the electron-emitting surface without operating the TWT is not now known.
Still other tests of a TWT and ancillary circuits may be carried out to advantage before such a device is completely operative. For example, the high voltage supply for TWT may be tested before the cathode of such a tube is activated or tests may be carried out to detect arcing within such a tube before the "ON" condition is attained.